The present invention relates generally to fuel delivery systems for engines, especially aircraft gas turbine engines, and more particularly to ecology and fuel flow splitting functions for such fuel delivery systems.
Some fuel delivery systems for gas turbine engines require multiple fuel manifolds to segregate various types of fuel nozzles for optimal engine performance. A means of dividing this flow between the manifolds is therefor required. U.S. Pat. No. 5,809,771 Wernberg discloses an ecology valve and a fuel flow splitting valve having a single piston operable in two different regions, one for modulating flow to primary and secondary engine nozzles as a function of fuel pressure and another where flow to primary and secondary engine nozzles is determined by the fixed port geometry. It is very difficult to extend this concept to more than two distinct engine manifolds.
Some engines also require an ecology function that removes a set quantity of fuel from the engine fuel manifold(s) upon cessation of engine operation. Fuel removal is required for two reasons. First, it keeps fuel from vaporizing into the atmosphere. Second, it keeps fuel from coking on the engine""s fuel nozzles, a condition that hinders nozzle performance. Prior art ecology systems have used an arrangement of pistons, check valves, plumbing, reservoirs and pumps to accomplish this task. In engines requiring multiple fuel manifolds, multiple ecology valves or a multiple chambered ecology valve have been used. These types of architecture result in complex, high cost and weight ecology systems. A two chambered valve is disclosed in the above-mentioned Wernberg U.S. Pat. No. 5,809,771. In the Wernberg system, fuel is simultaneously withdrawn from the two manifolds and a separate chamber is required for each engine manifold to ensure discrete fuel removal from those manifolds upon engine shut-down. It is also very difficult to extend this concept to more than two distinct engine manifolds. The Wernberg system employs at least one check valve downstream of the ecology valve for diverting a part of the modulated flow from the primary to the secondary manifold. Such downstream valving allows a degree of undesirable cross-talk between the manifold supply lines and may reduce engine fuel flow reliability or increase the load on the fuel supply pump.
It is desirable to minimize the fuel remaining in an engine fuel manifold upon cessation of engine operation and to provide a compact, economical ecology function for fuel supply systems. It is also desirable to achieve such an ecology function by employing a simple single diameter piston valve which is controlled solely by a signal from a pressurizing valve, and to accomplish the ecology function while avoiding any cross-talk between the several manifold fuel supply lines thereby maintaining the fuel pressure integrity in those several lines. It is further desirable to avoid this cross-talk while achieving a fuel splitting function which is operable to appropriately distribute fuel to a plurality of engine fuel manifolds.
The present invention provides solutions to the above problems in the form of a fuel divider and ecology system adapted for an engine requiring three discrete fuel manifolds. One manifold contains atomizer nozzles (for engine start), and two manifolds contain air blast nozzles, one servicing the lower half and the other servicing the upper half of the engine. For the flow dividing function, the system incorporates a plurality of valves to appropriately distribute metered burn flow to these three fuel manifolds. This system accomplishes the ecology function using one single chamber staged valve, and modifying the main fuel control pressurizing valve to include a pressure switching function. This approach limits the ecology components to one ecology valve piston, and one plumbed line from the pressurizing valve to control it. The fuel splitting function is achieved by a first splitter valve which divides the fuel flow from a pressurizing valve between atomizer or start-up nozzles and air blast or main running nozzles; and a second splitter valve which subdivides flow between the upper and lower manifolds.
In accordance with one form the invention, an ecology valve for minimizing the accumulation of fuel in a multiple fuel manifold engine system when the engine is shut down has a control port coupled to and controlled solely by an engine fuel system pressurizing valve and a housing with a piston reciprocable therein between first and second extreme positions. The piston defines, in conjunction with the housing, a variable volume chamber for sequentially withdrawing fuel from each of the engine fuel manifolds when the engine is de-energized and the piston moves from the first extreme position toward the second extreme position thereby purging the manifolds of fuel. There is a spring within the housing which supplies a force to the piston to urge the piston toward the second extreme position and the piston responds to high pressure at the ecology valve control port overpowering the spring to move toward the first extreme position. There are a plurality of sidewall or ecology ports in the housing selectively opened and closed by piston movement to couple the variable volume chamber and selected fuel manifolds.
In accordance with another form of the invention, an improved fuel flow dividing arrangement is located intermediate a pressurizing valve and a plurality of engine fuel manifolds for appropriately distributing fuel flow among the manifolds. The arrangement includes a concatenated pair of two-way splitter valves one of which distributes fuel flow between an atomizer nozzle manifold and the remaining manifolds. Another splitter valve distributes the down stream fuel flow from the first splitter valve between upper and lower air blast nozzle manifolds. The second splitter valve provides a pair of low volume fuel flow paths to the upper and lower manifolds during engine start-up and a second pair of high volume fuel flow paths to the upper and lower manifolds during normal engine running conditions. There is a head effect fuel flow restricting valve in the low volume fuel flow path to the lower manifold to compensate for elevation difference induced low burn rate fuel flow differences between the upper and lower manifolds. The first splitter valve provides a low volume fuel flow path to the second splitter valve during engine start-up and a second high volume fuel flow path to the second splitter valve during normal engine running conditions, and switches fuel routed to the atomizer nozzles from pressurizing valve discharge pressure to the lower manifold pressure.